The present invention relates to a knocking sensor using a piezoelectric element.
There has been known a knocking sensor that detects a knocking phenomenon in an internal combustion engine of an automobile or the like, and a retard control of an ignition timing of an ignition plug is conducted according to the detection of the knocking sensor.
As the above-mentioned knocking sensor, there has been known a knocking sensor of a so-called sensor hole non-resonant type having an installation hole for installation to a cylinder block of the internal combustion engine in a center portion thereof. The knocking sensor includes a metal shell having a cylindrical portion and a flange portion located on one end of the cylindrical portion, and is configured so that an annular insulating member, a piezoelectric element, a weight, and a nut are fitted into an outer periphery of the cylindrical portion in order from the flange portion side. Then, an external thread portion of an outer peripheral surface of the cylindrical portion is screwed into the nut to lock the weight, and the piezoelectric element is fixedly interposed between the flange and the weight. Further, an overall inner part into which the insulating member, the piezoelectric element, and the weight are incorporated into the metal shell is coated with a resin to configure the knocking sensor. An inner surface of the cylindrical portion forms the installation hole. See for example, JP-A-2010-101696.